INTRODUCTION Industrial sectors play an important role in the growth of the world economy by providing services and products that improve the quality of people's lifestyle. However, the rapid industrialization generates huge amounts of wastes which greatly affect the environment. The increasing amounts of industrial wastes require a larger space of landfill and expensive treatment for disposal. This causes a detrimental pollution effect on the soil, water and air 1 . One of the industries that generate quite large amounts of industrial waste is the pulp and paper production. This industry produces large amount of sludge as a result from their wastewater treatment plant. The primary method of disposal for paper mill sludge is mainly through land application and land filling 2 . Land filling costs are rising because of stringent regulation, taxes and declining capacity. With landfill space becoming scarce and expensive, sludge are being burned or incinerated to reduce their volume and to recover part of the energy that they contain 3 . Expensive treatment of land disposal necessitates other means of treatment which is more economical and other alternatives used of these waste for beneficial application. Removal of Phosphate by Paper Mill Sludge: Adsorption Isotherm and Kinetic Study SHARIFAH MOHAMAD 1,* , NOR KARTINI ABU BAKAR 1 , AHMAD RAZALI ISHAK 1,2 , HEMAVATHY SURIKUMARAN 1 , KAVIRAJAA PANDIAN 1 , MUGGUNDHA RAOOV 1,3 , NUR NADHIRAH MOHAMAD ZAIN 1,3 and KUMUTHINI CHANDRASEKARAM 4 1 Department of Chemistry, Faculty of Science, University of Malaya, Kuala Lumpur 50603, Malaysia 2 Department of Environmental Health, Faculty of Health Science, University of Teknologi Mara, Puncak Alam, 42300 Kuala Selangor, Malaysia 3 Cluster Integrative Medicine, Advanced Medical & Dental Institute, Universiti Sains Malaysia, No 1-8 (Lot 8), Persiaran Seksyen 4/1, Bandar Putra Bertam, Kepala Batas, Pulau Pinang 13200, Malaysia 4 University of Malaya Centre for Ionic Liquids, Department of Chemistry, Faculty of Science, University of Malaya, Kuala Lumpur 50603, Malaysia *Corresponding author: Fax: +60 3 79674193; Tel: +60 3 79676751; E-mail: sharifahm@um.edu.my Received: 24 August 2013; Accepted: 25 November 2013; Published online: 5 June 2014; AJC-15292 Phosphate ions have been removed from aqueous solution by paper mill sludge. The influences of experimental conditions such as pH, amount of adsorbent, initial concentration of phosphate, adsorption isotherm and adsorption kinetics of paper mill sludge were studied. The adsorption of phosphate was more efficient in the basic pH region (pH 12). Pseudo second-order model fits better than the pseudo first-order model for adsorption kinetic data and indicates the adsorption process is based on chemisorptions. The calculated activation energy (Ea) is 37.01 J/mol which further suggests that the sorption of phosphate by paper mill sludge was based on chemical adsorption. Consequently, the equilibrium isotherm data were fitted well to Langmuir isotherm with maximum adsorption capacity of 12.65 mg/g. From the study, it showed that paper mill sludge has the potential to be utilized as a cost effective and high capability adsorbent for removal of phosphate from aqueous solutions. Keywords: Paper mill sludge, Phosphate, Removal, Kinetics, Adsorption. A recent alternative method to overcome this problem is by utilization of the industrial waste for other valuable appli- cations. This alternative method allows the industrial sector to reduce the cost of disposal and at the same time reduces the cost of the manufacturing process, enhances the efficiency of resource utilization and most importantly reduces the negative impacts on the environment and human health. Utilization of waste material for other valuable applications will balance the increasing demands of limited natural resources by providing alternative resources and reduces the dependency on natural resources 1 . Paper mill sludge is mainly composed of organic matter which is added to the paper or pulp whereas inorganic compounds (mainly calcium carbonate, kaolinite and talc) are used as fillers and coating 4 . Some studies had been done using material conta- ining calcium such as fly ash and calcite to remove phosphate from waste water 5 . In view of the fact that the calcium content in the paper mill sludge is high, hence we investigated the efficiency of paper mill sludge as adsorbent for removal of phosphate from aqueous solution. Phosphate wastes are usually being discharged into rivers causing harmful effects to the environment and human health 6 . The excess of phosphate will ASIAN JOURNAL OF CHEMISTRY ASIAN JOURNAL OF CHEMISTRY Asian Journal of Chemistry; Vol. 26, No. 12 (2014), 3545-3552 http://dx.doi.org/10.14233/ajchem.2014.16227